I took it apart, even removed the top and bottom covers, but it’s just impossible to see what is in there in the media compartment that might cause the marks. I even powered it up while it was apart and put one of my “coasters” in. It ran as silent as ever, but after a few minutes when I looked at the disc I could see the faint marks starting to show. Ran it a few more minutes and the marks got more pronunced.
Considering the cost of these burners I don’t think it is worth pursuing. But it has put me off NEC. As I said before, both my son’s 2550 and this 3500 are doing the same thing. And I’ve already replaced it with a Lite-On.
If anyone reading here is from NEC, I’ll gladly let you have the unit to see what’s wrong … as long as you pay for the shipping.
Thanks for your input.